Once ramakrishna asked his disciples to steal a little rice from their own home but there was one condition that nobody sees them stealing rice. After a week all of his disciples came back with rice except for one. Everyone was happy as they were able to complete task given to them of stealing rice from home without anyone noticing them. Ramakrishna asked that student reason for coming empty handed. Student told him that even if he tries hard to steal rice hiding from everyone else, he always saw himself stealing rice. So there was never ever a situation when he could have steal rice when nobody is seeing.. Because what ever we do, it is never hidden from one person and that is our-self. That student who came empty handed was swami vivekananda. 
Whenever we try to do something wrong, even if we hide it from everyone else yet we can't hide it from our-self. So we should never do anything wrong. 